Alkaline cells are well known in the art and generally employ a zinc anode, a manganese dioxide cathode and an aqueous solution of potassium hydroxide for the electrolyte. These cells are readily available commercially for industrial and home applications. Recently a new type of alkaline cell was disclosed by Cegasa International, a Spanish company, and referred to an air assisted cell. This type of cell employs a zinc anode, manganese dioxide cathode, and aqueous solution of potassium hydroxide as the electrolyte. The cell is designed so that the positive electrode containing the manganese dioxide is exposed to air so that air distribution passages are provided to alloy air from the atmosphere to enter the cell and contact the manganese dioxide. In conventional alkaline cells, the manganese dioxide is shielded from atmosphere (air) through hermetical seal means. The components of the air assisted cell that have been added or modified to permit air to contact the manganese dioxide, occupies space in the cell that could be used for additional active components in a fixed volume size cell. Maximum power output of a cell would require maximum amounts of the active components to be assembled in the cells. In the case of conventional alkaline cells, the manganese dioxide is generally made with a low porosity manganese dioxide material so that the maximum amount of manganese dioxide can be assembled into the cell. In U.S. Pat. No. 5,079,106, an improved air assisted alkaline cell is disclosed in which the cathode for the cell is a mixture of a porous manganese dioxide material and a substantially less porous manganese dioxide material. An experimental alkaline cell was compared with the improved air assisted alkaline cell in this reference and the comparison recited in this patent was that the experimental alkaline cell had better discharge capability on high rat drains since the cathode material present in the assisted alkaline cell had less manganese dioxide than that of the experimental alkaline cell.
U.S. Pat. No. 5,277,890 relates to the manufacture of manganese dioxide by a chemical process. The resulting manganese dioxide product takes the form of particles characterized by filament-like protrusions jutting out from its surface. The manganese dioxide particles having such surface features can be manufactured by reacting manganese sulfate with sodium peroxodisulfate in aqueous solution. The process can be controlled to yield high density manganese dioxide. The manganese dioxide formed in the process can be deposited directly onto the surface of electrolytic manganese dioxide (EMD). The manganese dioxide product is particularly suitable for use as a cathode active material in electrochemical cells.
It is an object of the present invention to provide a sealed alkaline cell that employs a manganese dioxide cathode that is composed of a minor amount of a highly porous manganese dioxide material mixed with a low porosity manganese dioxide material and the cell is provided with seal means to effectively prevent air (oxygen) entering from the atmosphere.
It is an another object of the present invention to provide a sealed alkaline cell that employs a manganese dioxide cathode wherein the manganese dioxide component is composed of a minor amount of chemically synthesized manganese dioxide (CMD) and a major amount of electrolytically deposited manganese dioxide (EMD).
It is another object of the present invention to provide a sealed alkaline cell having a manganese dioxide cathode comprising a highly porous manganese dioxide material and a low porosity manganese dioxide material and wherein the weight percent of the highly porous manganese dioxide material is between 1 wt. % to 35 wt. % of the low porosity manganese dioxide material.
The above and further objects will become apparent upon consideration of the following description and drawing thereof.